Phineas and Ferb build a shrinking submarine so they can go inside Isabella's dog and retrieve a sash the pet ate, but they accidentally end up in Candace's stomach instead. Meanwhile, Perry must stop Doofenshmirtz from destroying people who can't make up their mind.

The boys locate their parents' favorite band, Love Handel, to perform a reunion concert in the backyard to make up Dad forgetting his wedding anniversary. Meanwhile, Doofenshmirtz plans a surprise birthday party for his daughter, Vanessa.